1. Field of the Invention
The invention relates generally to methods and apparatus for dispensing a viscous material on a substrate, such as a printed circuit substrate.
2. Discussion of Related Art
There are several types of prior art dispensing systems or dispensers used for dispensing metered amounts of liquid or paste for a variety of applications. One such application is the assembly of integrated circuit chips and other electronic components onto circuit board substrates. In this application, automated dispensing systems are used for dispensing dots of liquid epoxy or solder paste, or some other related material, onto circuit boards. Automated dispensing systems are also used for dispensing lines of underfill materials and encapsulents, which mechanically secure components to the circuit board. Underfill materials and encapsulents are used to improve the mechanical and environmental characteristics of the assembly.
FIG. 1 schematically illustrates a known dispenser, which is generally indicated at 10. The dispenser 10 is used to dispense a viscous material (e.g., an adhesive, encapsulent, epoxy, solder paste, underfill material, etc.) or a semi-viscous material (e.g., soldering flux, etc.) onto an electronic substrate 12, such as a printed circuit board or semiconductor wafer. The dispenser 10 may alternatively be used in other applications, such as for applying automotive gasketing material or in certain medical applications. It should be understood that references to viscous or semi-viscous materials, as used herein, are exemplary and intended to be non-limiting. In one embodiment, the dispenser 10 includes first and second dispensing units or heads, generally indicated at 14 and 16, respectively, and a controller 18 to control the operation of the dispenser. Although two dispensing units are shown, it should be understood that one or more dispensing units may be provided.
The dispenser 10 may also include a frame 20 having a base or support 22 for supporting the substrate 12, a dispensing unit gantry 24 movably coupled to the frame 20 for supporting and moving the dispensing units 14, 16, and a weight measurement device or weigh scale 26 for weighing dispensed quantities of the viscous material, for example, as part of a calibration procedure, and providing weight data to the controller 18. A conveyor system (not shown) or other transfer mechanism, such as a walking beam, may be used in the dispenser 10 to control loading and unloading of substrates to and from the dispenser. The gantry 24 can be moved using motors under the control of the controller 18 to position the dispensing units 14, 16 at predetermined locations over the substrate. The dispenser 10 may include a display unit 28 connected to the controller 18 for displaying various information to an operator. There may be an optional second controller for controlling the dispensing units.
Prior to performing a dispensing operation, as described above, the substrate, e.g., the printed circuit board, must be aligned or otherwise in registration with a dispensing unit of the dispenser. The dispenser further includes a vision system 30, which is coupled to a vision system gantry 32 movably coupled to the frame 20 for supporting and moving the vision system. Although shown separately from the dispensing unit gantry 24, the vision system gantry 32 may utilize the same gantry system as the dispensing units 14, 16. As described, the vision system 30 is employed to verify the location of landmarks, known as fiducials or other features and components, on the substrate. Once located, the controller can be programmed to manipulate the movement of one or both of the dispensing units 14, 16 to dispense material on the electronic substrate. The dispense operation may be controlled by the controller 18, which may include a computer system configured to control material dispensers. In another embodiment, the controller 18 may be manipulated by an operator.
In some embodiments, the dispenser 10 may operate as follows. The circuit board may be loaded into the dispenser 10 in a depositing position using the conveyor system. The circuit board is aligned with the dispensing units 14, 16 by using the vision system 30. The dispensing units 14, 16 may then be initiated by the controller 18 to perform a deposit operation in which material is deposited at precise locations on the circuit board. Once the dispensing units 14, 16 have performed a depositing operation, the circuit board may be transported by the conveyor system from the dispenser 10 so that a second, subsequent circuit board may be loaded into the material deposition system. The dispensing units 14, 16 may be constructed to be quickly removed and replaced with other units. The dispenser 10 is capable of dispensing material on only one side of the circuit board.
Sometimes, it is desirable to dispense such materials on both sides of the substrate. One such dispenser is offered by Protec Co., Ltd of Incheon, Korea, and incorporates a substrate support that rotates about an axis that is transverse to a direction that the substrate travels through the dispenser. With this dispenser, belts that engage edges of the substrate move the substrate through the dispenser. With this arrangement, it is difficult to dispense material near edges of the substrate since the belts interfere with the dispensing unit when attempting to dispense material near the edges of the substrate.